Ignition system



May 22, 1945.I A. A. KAsAJlAN 2,376,362

IGNITION SYSTEM 4 4 v Filed April r2, 1942 "j I www/2' Ihm mi Wzl/4m v ,Y/mg

l u ATTORNEY Patented May 22, 1945 asrassz OFFICE IGNITION SISTEM ArmenA. Kasarjian, Elmhurst, NQY.

l Appunti@ April 2,1942, serai No. 431,336

-s claims. (o1. sis-sii i This invention relates to ignition systems :for internal combustion engines and to spark plugs adapted for use in such systems:

In the usual ignition systems for internal combustion engines, a .spark plug is commonly employed having spaced electrodes forming a gap across which a spark is caused to jump inl order to ignite the gaseous charge in the cylinder. In theory, it is necessary to provide a sumciently high voltage to ionize the gases atthe gap. When such ionization'occurs, there is a discharge of electrical'energy across the gap to form the spark. y

In practice, such ignition systems include a source of electrical energy such as a magneto or battery, a primary and secondary coil, and some form of circuit breaking device for interrupting theiiow of current from the source to the primary. When the supply of current to the primary isAin- Vterrupted, the voltage in the secondary increases until it reaches a point suil-ciently high to ionize the gases at the gap, and anoscillating, high voltage capacity discharge occurs which quickly discharges'some lof the accumulated electrical energy and greatly reduces the voltage of the re- However, since the gap has been ion-` ized, the lower voltage is still sufficient to bridge' mainder.

the gap and a continuous current arc is established between the electrodes. This arc continues until the accumulatedelectrical ,energy is spent. In the art, the high voltage capacity discharge has ybeen referred to as the capacity component of the spark, and the subsequent low voltage current discharge has been referred to as the inductance component or tail of the spark. It has been generally recognized that the inductance component is of no material value for ignition purposes,

yand is, in fact,'undesirabie because it causes .erosion of the electrodes.

, Heretofore it has been proposed tov place a condenser of` relatively small capacity in series with the spark plug in order to eliminate the inductance component, 'and to cause the accumulated energy to be discharged in the form of a series of `capacity components. Such condensers have been referred to in the art as convert/ers, cur- Ireni; transformers," interrupters",and the like.

Such condensers serve to arrest the flow of current at the gap immediately after the initial capacitydischarge has taken place due to the reduction in voltage causedl by such' discharge.

A Thereafter, the voltage of the remaining energy increases until a second capacity discharge takes place, and so on until the energy is spent inthe form of a series of such capacity discharged. 4 While the theory underlying the use'cf such condenser-s apeared correct, lt was noted that the improvement in the performance of ignition systems in which they were incorporated was negligible. Asa result, their use' has been generally discontinued.

I have discovered that one reason for the lack of Vimprovement lay in the fact that the capacity of the usual ignition systems with which such condensers were used was relatively small. Consequently, the intensity of the individual capacity discharges which took place was relatively weak. It is an object of the present invention, therefore, toemploy such a condenser in an ignition system of relatively large capacity, in order to provide a series ci capacity discharges of high intensity.

It is a further object of the 'invention to provide a spark plug particularly adapted for use in I plug particularly adapted for use in such a system.

Figure 3 is a similar vertical section 0i the lower end of a plug showing-a modified type of insulation.

According to the present invention I. propose to increase the capacity oi the ignition system by providing an additional condenser of relatively large capacity, which said condenser is connected in parallel with the spark plug. This is illustrated diagrammatically in Figure l, in which i is a source of electrical energy and 2 is a primary coil connected thereto, the primary circuit including any suitable means for interrupting the flow of current to the primary coil, such as `a circuit breaker 3 operated Iby a cam 4, the usual conbreaker. The secondary circuit includes the secondary coil 8 and the spacedielectrodes 1a and Ib of the spark plug. Connected in series with the spark plug is a condenser 8 ot relatively small capacity which has heretofore been referred to as a "converter," and connected in parallel .with the spark plug and across the'spark'plug and the condenser 8 is a condenser 9 of relatively large climacity.l For example, the condenser 8 may have a 'capacity of about 'liammn and the condenser 9 may have acapacityoiabout 20 mmf. Iorgood results. In this connectiomit may be: noted that in some ignition systems, and particularly in ignition systems adapted for use in aircraft engines, in order to avoid radio interference, it is now the practice to shield the high tension cables leading from the secondary to the spark plugs by surrounding said cables with a metallic jacket. In fact, spark plugs adapted for use in such shielded systems are themselves shielded by the provision of an outer metallic jacket. It will, of course, be obvious that such shielding jackets serve as condensers of relatively large capacity, for such jackets as used in shielded systems ordinarily have a capacity in excess of 150 mmf.

Since such shielding jackets are grounded, they are connected to .the ignition system in parallel with the spark plug in the manner shown in Figure 1. Thus in shielded systems 'such shielding ing provided with a thread I5 adapted to receive a threaded coupling connecting the plug to the shielding of the cable.

Extending axially of the shell il is a central spindle I6 terminating at its lower v end 'ina flanged head |1 constituting one of the electrodes of the plug. I'he said spindle is preferably made of alloy steel and along a portion of its length is surrounded by a copper sleeve I 3 adapted to con- -duct heat rapidly away from the flanged head I1.

' The spindle is separated from the shell Il by suitable insulation, comprising preferably awrapjackets serve admirably as the additional condenser 9. In unshielded systems, however, a separate condenser must be provided, and connected vin parallel as shownin Figure 1.

'I'he system described is particularly well adapted for use in aircraft engines due to the exacting requirements imposed by the nature of such engines, i. e., extreme high compressions, high temperatures, high speed, and the requirement for reliable performance and longlife of the ignition system and of the spark plugs employed in such engines. Because of the intensity of the spark produced by the above described system, I have found it possible to safely reduce the size of the spark gap of the usual spark plugs used in such engines, and thereby secure important advantages of increased reliability and increased life. Heretofore it has been the accepted view that the spark gap in spark plugs for aircraft engines should not be less than .012, because it was found by experience that a smaller gap would quickly foul by the accumulation of carbon, particularly when the engine was idling or running at low speed. Such fouling, resulting in parasitic losses -at the gap, soon prevented the plug from firing. By causing sparks to be formed as a series of capacity discharges of high intensity, in accordance with my invention, I find that such sparks will burn on any accumulations of carbon which may tend to form on the electrodes, and that it is possible, therefore, to reduce the gap to .010" .or less. For example, I have reduced the gap to as little as .003" with successful results, but mechanical limitationsA of design for commercial manufacture make this diiiicult in ordinary production. Therefore, for ordinary comthe engine is idled over a period of several hours.

I have also found it possible to utilize a newtype of spark plug to advantage'in such systems, such plug being illustrated in Figure 2. The said plug is of the shielded type, adapted for connection to a shielded cable performing the functions 'of the condenser I9 ofthe diagram of Figure l,

and said plug includes within its structure a condenser or converter performing the functions of the condenser 8 of Figure 1. f

' 'I'he said plug comprises an outer'shell having its lower portion threaded to screw"iinto a cylinder head of an engine. Y Above the threaded portion is an enlarged portion having va flange I2,

`adapted to seat against a gasket, and 'a hexagonal portion I3 adapted to nt a wrench. i Above the ens, larged portion is a tubular portion I4 constituting the shieldingof the plug, this tubular portion be-` ping of cigarette mica I9 extending substantially from the upper end of the spindle to the lower end. At the extreme lower end of the spindleand lying flush with the upper surface of the flanged head I1 is an annular disk 2| of insulating material, preferably mica washers,- which spaces the head from the annular` ring 22 which constitutes the other electrode. v'I'he thickness of the disk 2| determines the gap between the electrodes, which, as previously stated is preferably less than .010". The inside lower corner of the ring 22 is cut away as shown to provide `an annular space'for the reception of refractory ceramic insulating material 23 in plastic form to prevent parasitic losses as described in my prior Patent No. 1,958,580, dated May 15, 1934.

Additional insulation is provided at the ,upper end of the spindle, preferably vin the form of a stack of mica washers 24 surrounding the'cigarette mica. The lower end of the stack rests on the upper ends of the conical sealing members 25 iand 26 and the yupper end of the stack is held in place by the anged end 21 of the spindle, a steel ring 28 being interposed therebetween. The inner wall of the lower end of the shell Il is linedA ignition, lbut can only be usedto advantage in a plugv of this type in an ignition system as above described. In an, ordinary ignition system .the danger of fouling would be so great asto outweigh the advantage of rapid cooling.

Additional insulation is also provided at the upperend of the plug vwithin the tubular portion |4. This is in the form of cigarette mic'a 3|- A extending from the upper` end of 'the tubular portion I4 to the lower end of the stack of mica washers 24. 'Ihe said cigarette mica is preferably contained in athin itsupper end turned over themi'ca in place. e e

Carried within the tube 3|, 32 and in contact as shown at 33 to hold with the end of the spindle IB is the condenser or converter previously referred to, and corresponding to the 4condenser 8 of Figure 1. As

shown, said condenser comprises a series of metal washers 34 spaced by mica washers 35, said metal washers and' mical washers being surrounded and encased in a wall of any 'suitable insulating material such as ceramic material 38 so that the condenser maybe handledas a unit and easily replacedr if necessary. The said condenser is held in contact with the end of the spindle by the usual spring lfitting used to con-l i' nect the plug to the cable.

In the modied form of plug shown in Figure 3, theA mica washers 2| brass-tube s2 having have been omitted and an annular sleeve 4l o suitable refractory ceramic material in solid form is seated in the electrode ring 22,`the lower end of said sleeve engaging the anged head. i1 as shown. In this case the height of the sleeve determines the gap between the electrodes, which, as previously stated, is less than .010". The said sleeve may also be coated with refractory ceramic material in plastic form to prevent parasitic losses as previously described.

It will be understood that the invention may he variously modied and embodied within the scopew of the subjoined claims.

I claim as `my invention:

l. In an ignition system for internal combustion engines, a secondary circuit including a spark plug, a .secondary coil, a condenser of relatively small capacity connected in series with said spark plug, and a condenser of relatively large capacity connected across said spark plug and said condenser of relatively small capacity.

2. In an ignition system for internal combustion engines, a secondary circuit including a spark plug, a secondary coil, a condenser of rela-v y tively small capacity connected in series with said spark plug, a cable connecting said spark plug and said secondary coil, and a metallic shielding surrounding said cable, said metallic shielding constitutinga condenser of relatively large capacity connected across said spark plug and said condenser of relatively small capacity.

" 3. In an ignition system for internal combustion engines, a secondary circuit including a spark plug, a secondary coil, a condenser of relaf tively small capacity. connected in series with said spark plug, and a condenser of relatively large .capacity connected across said spark plug and said condenser of relatively small capacity, said spark plug having electrodes spaced to provide a gap less than .010".

4. In an ignition system for internal combustion engines, a secondary circuit including a spark plug, a secondary coil. a condenser of relatively small capacity connected in series with said spark plug, and a condenser of relatively large capacity connected across said spiark plug and said condenser of relatively small capacity, said spark plug having electrodes spaced to provide a gap of approximately .00

5. In an ignition system for internal combustion engines, a secondary circuit including a spark plug, a secondary coil, a. condenser of relatively small capacity connected in series with said spark plug, a cable connecting said spark plug and said secondary coil, and a metallic shielding surrounding said cable, said metallic shielding constituting a condenser of :relatively large capacity connected across said spark plug.

and said condenser of relatively small capacity, said spark plug having electrodes spaced to provide a gap less than .010.

6. In an ignition system for internal combustion engines, a secondary circuit including a.

spark plug, a secondary coil, a condenser of relatively small capacity connected in series with said spark plug, a cable connecting said spark plug and said secondarycoil, and a metallic shielding surrounding said cable, said metallic shielding constituting a condenser of relatively large capacity connected across said spark plug and said condenser of relatively small capacity, said spark plug having electrodes spaced to provide a gap of approximately .007".

, ARMEN A. ,KASARJIAN 

